DIY advice: rendering, tiling and removing polystyrene ceiling tiles

Jeff Howell solves your building problems.

By Jeff Howell

11:13AM GMT 03 Feb 2009

BRICKWORK SOLUTIONS

Q In our 1908 Victorian semi, we have a small, well-ventilated cellar, upon which I’d like to effect a DIY renovation. The render on the walls is in poor repair: flaking, falling off in chunks and suffering from what appears to be efflorescence pushing through the surface from the brickwork. Even the concrete floor is breaking up, so my plan is to rake off the render back to bare brick and then treat the brickwork and probably just patch the floor. Instead of splashing out on expensive chemical sealants, my thoughts were to “tank” the exposed brickwork (which I understand to mean paint on a bituminous layer) on top of which I’d then put on a layer of a masonry paint to provide a decent looking finish. My biggest concern is whether this treatment will work, or last? AP, Lichfield

A Your DIY plan might work, but it probably won’t. I’d put its chances of success at no higher than 5 per cent. Efflorescence (the formation of salt crystals) is a symptom of the movement of water from one place to another – so it sounds likely that yours is a true underground cellar, with groundwater penetrating laterally from outside to in.

Therefore any type of sealant applied to the inside wall surfaces will be subject to being blown off by the crystal salt formation, and possibly also by hydrostatic pressure – the force of the water coming in through the walls. The only type of tanking able to withstand these pressures would be professionally-applied mastic asphalt, and even this should ideally be finished internally with a “loading coat” consisting of a skin of brickwork.

These are stiff, “dimpled” plastic membranes that fix to walls and floors, and can be plastered over directly, or insulated and lined with a variety of board materials. They do not stop water from penetrating, but provide an air gap that allows it to evaporate or drain away without damaging the decorative surface. In very wet conditions, a surface drain or sump pump system may be required, but in most situations, ventilation using airbricks is sufficient.

TILING MISTAKE

Q We have recently had to retile the mid section of an extensive cottage-style property. The new tiles look very bright in comparison to the flanking roof sections on both sides. I am told that a mixture of milk and yogurt sprayed onto the new tiles will encourage lichen. Do you have any ideas of the recipe and how to apply? DA, Driffield

A Sorry to be offering you wisdom after the event, but you really shouldn’t have done it like that. New roof tiles will always look brighter and cleaner than old ones, and no amount of artificial weathering or lichen growth will disguise the fact. When re-covering a section of an existing roof, or adding an extra section of roof, the correct practice is to take off all the existing tiles, “shuffle” in the new ones on a random basis, and retile the whole area. That way the bright colours and sharp edges of the new tiles are distributed evenly across the whole roof elevation. Any experienced roofing contractor should know this. As regards encouraging lichen growth with milk or yogurt, I suspect this is something of an old wives’ tale, as the first heavy rain would wash it all off anyway.

CEILING STRIPPING

Q I have recently purchased a bungalow, most rooms of which have polystyrene ceiling tiles. How can I remove these without doing the ceiling any damaging? WC, Milford Haven

A Polystyrene (known as “Styrofoam” in the US) is a good example of how a material with good thermal insulation properties can also have drawbacks.

Firefighters hate polystyrene ceiling tiles because in house fires they melt and drip blobs of burning plastic, and also give off carcinogenic fumes. Many chartered surveyors advise their removal. And yet, even now, there is an apparent resurgence in the fashion for lining walls with thin sheets of the stuff, albeit in versions advertised as “flame retardant”.

The ease of removing polystyrene ceiling tiles is inversely proportional to the diligence (and quantity of adhesive) with which they were applied. You may be lucky and find that they come off easily with a flat-bladed scraper. But there is always likely to be some surface damage and some residual adhesive – best removed by softening with a steam wallpaper stripper, and scraping. Be prepared for a lot of filling and sanding, before finishing the ceiling with 1000-gauge lining paper and emulsion paint.